The invention relates to a metallic flat gasket with a passage opening, which is covered by a filter element. The gasket thus on the one hand serves for the sealing of a transition of a pipe between two parts and on the other hand for catching particles, which are comprised in the fluid streaming through this pipe.
In the state of the art, it has been tried to provide gaskets with a filter effect in that an entire gasket layer from a filter material is installed in the gasket between at least two metal sheet layers, in particular from a woven material and in that the areas surrounding the filter areas are filled with a sealing material, e.g. with an elastomer, as is described in DE 10 2007 019 946 A1. Such filters can only be used in a very limited temperature range because of the filling material, so that they are not suited for applications with hot gases. Further, the production process of the multi-layered gasket is very laborious.
In the same way, it has been tried to produce gaskets with filters in that the holes of the filter are directly introduced into the gasket layer, e.g. using etching or using laser, as this is for instance described in DE 10 2009 010 385 A1. This ascertains a good stability of the filter layer. However, doing so, often holes are produced which are too large. Further, the methods are very time-consuming so that the gaskets cannot be produced in the cycle times required and in an allowable cost frame.
Often, in addition, the installation space available for the filtration is very small as the cross-sectional area of the fluid passage to be filtered is very small. Furthermore, the filter elements formed only in the plane of the gasket cause an unacceptably high pressure drop of the passing fluid. DE 10 2009 010 385 A1 shows embodiments where the gasket layer in the area of the filter is formed out of the plane in a cylinder-shaped manner so that not only the basic area of the cylinder but also the lateral walls produced by this shaping are available as filter area, so that the pressure drop is reduced. In addition to the disadvantages of this approach for the filter integration already mentioned, the shaping of the material causes a reduction of the metal sheet thickness in the areas affected, which causes that the metal sheet, into which the holes have been formed, no longer provides the structural stiffness required.
The same is true for the filter bowls made from woven filter mentioned in DE 20 2014 102 014 U1, which are connected to a layer of the metallic flat gasket via a clamping ring or through folding over of the edge regions of gasket layer and filter element one around the other. Here, the freely protruding woven filter does not provide sufficient structural stiffness in order to prevent elongations caused by the high pressures and temperatures of the fluid passing through it. Consequences of this are an unregulatedly enlarged width of the filter element and therefore an unregulated filter effect.
Recently, this has been taken into account in gaskets with a filter insert made from a wire mesh, in that gaskets with filter bowls have been produced where in addition to an embossed, in particular beaded gasket layer and a simple deep-drawn filter bowl from a wire mesh, a frame-shaped support element is provided which is deep-drawn, too, and with which the filter bowl is kept in its position even when loaded with high fluid pressures. The laborious double deep-drawing process, namely of the sheet layer and of the filter element, here is required as both the bottom of the filter bowl and the frame of the support element are pronouncedly bent out of the plane of the flat gasket, to be more precise from the plane of the gasket layer in the surrounding of the filter element, in order to provide the filter area required on the one hand and in order to guarantee for a sufficient support of this filter bowl on the other hand. In addition to the resilient material of the beaded gasket layer, which cannot be reshaped by deep-drawing, one further needs the non-resilient material of the support element from a metal sheet which can be deep-drawn and which generally is more expensive than the resilient material required to form the elastic bead. Thus, almost twice as much material is required, as no permanently elastic sealing elements can be embossed into a metal sheet which allows deep-drawing.